A roller called an anilox roller is used as an ink metering roller in an inking unit. The anilox roller has a function of supplying and metering ink. The function is realized by a plurality of independent recesses (cells) 1a and 2a formed by a laser or mechanical processing on outer surfaces 1 and 2 of the roller composed of a metal or ceramic, as shown in FIGS. 1 and 2.
FIG. 3 shows a schematic arrangement of a flexographic printing machine. Ink 4 in ink pan 3 is transferred onto plate cylinder 6 by anilox roller 5. In this case, excess ink 4 is scraped off by doctor blade 7 in contact with anilox roller 5. Doctor blade 7 is made of steel, a resin, or the like. Only a necessary amount of ink 4 is transferred onto plate cylinder 6 while it is filled in the recesses formed on the outer surface of the anilox roller. An ink film is transferred from plate cylinder 6 to printing material 9 such as paper urged against plate cylinder 6 by the pressure of impression cylinder 8, thereby performing predetermined printing.
FIG. 4 shows a schematic arrangement of a keyless offset printing machine. In this case, ink 4 in ink pans 3 is transferred from fountain rollers 10 to anilox rollers 5. Ink 3 is transferred therefrom to ink forme rollers 11 made of rubber, and then is transferred onto plate cylinders 6. In this case, excess ink 3 is also scraped off by doctor blades 7 brought into contact with anilox rollers 5. Subsequently, ink films are transferred from plate cylinders 6 to rubber blanket cylinders 12 in contact with plate cylinders 6. The ink films are transferred from rubber blanket cylinders 12 to printing material 9 so as to perform predetermined printing.
Dampening water units 13 serve to form non-image area. More specifically, dampening water units 13 supply dampening water 15 using dampening rollers 14 onto the non-image area before ink is supplied to the plate cylinders, thereby preventing adhesion of the ink to nonimage area.
Accordingly, the ink transfer ability of anilox roller 5 having a large number of recesses formed on its outer surface greatly influences printing quality. According to a method of forming recesses on such an anilox roller, for example, a mother mold is urged against the outer surface of a mandrel such that recesses are sequentially formed from one end portion of the mandrel. Then, in order to provide wear resistance to the roller, the outer surface of the mandrel is plated with copper or chromium. According to another method, as described above, a ceramic is flame-sprayed on a mandrel and is grinded, and then recesses are engraved by a laser. Quadrangular pyramid-shaped or quadrangular frustrum pyramid-shaped recesses are often employed. In addition, the number of recesses is set to correspond to the number of lines formed on the outer surface of a mandrel at a rate of, e.g., 165 lines/inch, 180 lines/inch, or 200 lines/inch. The depth of each recess and the amount of ink to be transferred by an anilox roller are decreased with an increase in number of recesses. According to specific requirements of such recesses (cells), 1 high shape precision must be attained, and 2 ink is not easily peeled off by dampening water from anilox roller (in offset printing).
The following drawbacks are posed in a conventional anilox roller.
(1) Anilox rollers having recesses formed by a mother die
1 The shapes of recesses vary widely on a roller or between rollers.
2 The outer surface of a roller is worn out by a doctor blade, and the shapes of the recesses change upon use of the roller. Consequently, the ink storage amount of the recesses is gradually decreased and the density of a printing matter is changed.
3 In an arrangement wherein recesses are independent from each other, ink is rejected because of excessive dampening water, i.e., a stripping phenomenon is caused. Note that a normal depth of each recess is 15 to 14 .mu.m.
(2) Anilox rollers having recesses formed by a laser
1 Large-scale facilities are required to form recesses and rollers. PA0 2 If the outer surface of a roller is damaged, it cannot be repaired. Therefore, a new roller must be manufactured. PA0 3 Heat is generated between a doctor blade and an anilox roller because of friction. For this reason, a rubber roller in contact with the anilox roller is expanded. As a result, the nip width of the rubber roller must be adjusted. PA0 4 A stripping phenomenon is caused because of excessive dampening water.